Numerous dye systems have been employed to impart desired color to fibrous materials. These systems include dyestuffs (or dye systems) having quite distinct chemical compositions, uses and mechanisms of coloration.
A major field of dye use lies in coloration of fibrous materials. Such uses encompass literally thousands of different dyestuffs developed primarily over the past one hundred years to meet the specific requirements engendered by the wide variety of fabrics involved.
By the way of example, reference is made to the Chapter entitled "Dyes" in Kirk-Othmers' Encyclopedia of Chemical Technology (Interscience 1950) for a discussion of this field. There mention is made of the various fibrous materials (commonly classified as "natural"-- including cellulose-based fibers such as cotton; keratin-based fibers such as wool; and fibroin-based fibers such as silk--"man-made"-- including derivatives of natural fibers such as rayon--and "synthetic"--such as nylon, polyester and polyolefin fibers of non-natural derivation). Similarly, different types of dyestuffs useful with various of these fibers are mentioned and include: acid, basic, direct, sulfur, vat, leuco esters, azo, acetate, pigment, oxidation, natural and inorganic dyes.
In addition to this broad field of fibrous, there are allied or ancillary fields of dye application. Of these, the most important is the cosmetic industry. There, in particular, dyestuffs are utilized for coloration of hair, a keratinaceous material. In this field, still greater limits are placed upon the use of dye systems because of the need to avoid toxicity or other adverse affects on the subject's skin or hair.
While the foregoing is by no means complete, it is indicative of the long history of dyes, the variety of types of dyestuffs, mechanisms of dyeing and dye applications in this art. Despite this history, however, completely satisfactory dyeing has not always been achieved. Among the drawbacks of known dye systems are: the resistance of the dyed materials to fading; the resistance of the dyed materials to erosion of color by rubbing and the like; the degree of color imparted to the materials incident to dyeing; and/or the efficiency and ease with which dye is imparted to materials for their coloration.
Much effort has been expended in seeking improved means of dyeing fibrous materials. In general, however, the known means of facilitating and improving such dyeing processes have had only occasional and/or limited success. These means have often proven expensive, successful only for alleviation of some of the foregoing drawbacks and/or useful only with certain types of the foregoing dye systems.